1. Field of the Invention
The present invention relates to a glass ceramic composition containing a glass component in order that the glass ceramic composition can be fired at a low temperature, a sintered glass ceramic material obtained by firing the glass ceramic composition, and a multilayer ceramic electronic component including the sintered glass ceramic material.
2. Description of the Related Art
Examples of effective methods for miniaturizing electronic apparatuses include the use of multifunction electronic components in the electronic apparatus. Examples of multifunction electronic components include multilayer ceramic modules.
Multilayer ceramic modules include multilayer ceramic substrates. The ultilayer ceramic substrates may contain conductive leads for electrical connection and for constituting a passive element, such as a capacitor or an inductor. Furthermore, a variety of electronic components can be mounted on multilayer ceramic substrates.
Multilayer ceramic modules are small yet have multifunctionality. Thus, the use of the multilayer ceramic modules can achieve miniaturization of electronic apparatuses.
The demand for electronic apparatus operating at higher frequencies has been increasing in addition to the miniaturization described above. In this situation, it is desirable that multilayer ceramic modules for use in a high-frequency band include multilayer ceramic substrates having satisfactory high-frequency properties. Specifically, it is desirable that insulating ceramic layers constituting multilayer structures of multilayer ceramic substrates are composed of an insulating ceramic sinter having satisfactory high-frequency properties.
Japanese Unexamined Patent Application Publication No. 2000-344571 (Patent Document 1) discloses an insulating ceramic composition suitable as a sintered insulating ceramic material capable of satisfying the requirements. Patent Document 1 discloses an insulating ceramic composition with a ternary system of forsterite, calcium titanate, and spinel. The insulating ceramic composition in a more preferred composition range disclosed in Patent Document 1 has a Qf of about 38,000 GHz or more and a temperature coefficient of dielectric constant of about −80 to +40 ppm·° C.−1, Qf being defined by frequency (GHz)/dielectric loss(tan δ).
When the multilayer ceramic substrate for the multilayer ceramic module is produced, a firing step is performed. In the firing step, conductive leads provided with the multilayer ceramic substrate are co-fired.
The conductive leads in the multilayer ceramic substrate must have low electrical resistance in order that the multilayer ceramic module can be used in a high-frequency region without problems. Thus, each conductive lead needs to be composed of a metal, such as copper or silver, having low resistivity.
However, a metal such as copper or silver has a relatively low melting point. To produce a multilayer ceramic substrate by cofiring a green substrate and a green conductive leads composed of the metal, an insulating ceramic composition for forming insulating ceramic layers constituting the multilayer ceramic substrate must be able to be fired at a low temperature, e.g., about 1,000° C. or lower.
Patent Document 1 discloses the insulating ceramic composition fired at a firing temperature of about 1,140° C. to 1,600° C. That is, the requirement that an insulating ceramic composition can be fired at about 1,000° C. or lower is not satisfied.
Furthermore, in order to provide a multilayer ceramic substrate capable of operating at higher frequencies and to provide higher-density conductive leads, insulating ceramic layers contained in the substrate need to have a lower dielectric constant. Patent Document 1 does not disclose the specific value of the dielectric constant of the insulating ceramic sinter obtained by firing the insulating ceramic composition disclosed therein.
Patent Document 2 reports an insulating ceramic composition capable of being fired at about 1,000° C. or lower, having a low dielectric constant, and having satisfactory high-frequency properties. Specifically, International Publication No. WO2005/082806 (Patent Document 2) reports an insulating ceramic composition capable of controlling the temperature coefficient of a resonance frequency at a low level and obtaining a higher Qf value.
Specifically, Patent Document 2 discloses a glass ceramic composition containing a first ceramic powder mainly composed of forsterite; a second ceramic powder containing at least one ceramic powder selected from the group consisting of a ceramic powder mainly composed of calcium titanate, a ceramic powder mainly composed of strontium titanate, and a ceramic powder mainly composed of titanium oxide; and a borosilicate glass powder, wherein the borosilicate glass powder contains about 3 to 15 percent by weight of lithium in the form of Li2O, about 30 to 50 percent by weight of magnesium in the form of MgO, about 15 to 30 percent by weight of boron in the form of B2O3, about 10 to 35 percent by weight of silicon in the form of SiO2, about 6 to 20 percent by weight of zinc in the form of ZnO, and about 0 to 15 percent by weight of aluminum in the form of Al2O3.
However, there have been advances in the reduction in the thickness of ceramic layers constituting multilayer ceramic electronic components in recent years. Furthermore, there has been an increase in signal voltage. Thus, the material constituting the ceramic layers needs to have higher electrical insulation reliability.